Anodic Behavior of Steel in Enhanced Sulfate Solutions

Abstract Severe corrosion of post-tensioned tendons in Florida bridges utilizing pre-packaged thixotropic grout products were documented. In those cases, conventional causes of steel corrosion in tendons were not consistent with corrosion development. Good correlation between the presence of deficient grout, corrosion development, and enhanced sulfate ion concentrations was observed. An update on laboratory testing of steel wire in sulfate solutions representative of deficient grout pore water is presented. The test setup was made to determine if sulfates in alkaline solutions can depassivate steel or if early presence of sulfates in alkaline solution may provide conditions that would adversely affect stable passive film formation. In the open circuit potential condition for pH 12.5 and 13 solutions, sodium sulfate concentrations as high as 65,000 ppm did not show ability to depassivate steel. Sodium sulfate concentrations as high as 20,000 ppm in pH 13 solution did not show indication to destabilize passive film growth, but destabilization of passive film growth resulting in severe corrosion occurred in the presence of 20,000 ppm sodium sulfate in pH 12.5 solution. Tests in pH 12.5 sulfate solution resulted in active corrosion or localized pitting corrosion. Sulfate levels associated with corrosion development was consistent to ranges reported in the literature.